The present invention relates to a combustion state detection system for an internal combustion engine (hereinafter sometimes called the engine), or more in particular to a combustion state detection system for the engine in which a misfire can be detected in all operating areas of the engine where a positive torque is generated.
In the well-known technique disclosed in Japanese Patent Application Publication No. JP-A-58-51243, the engine operating conditions are detected by measuring the engine speed taking advantage of the relation between the engine speed and the torque generated by the engine thereby to detect a misfire indirectly. According to this technique, the engine speed is detected at two or more ignition points within a single ignition cycle from the previous ignition point to the current ignition point, and the change in engine speed is determined from the difference in engine speed at different ignition points within the single ignition cycle. The engine speed changes thus sequentially determined are processed statistically, and the combustion state of the engine is judged using the result of the processing.
In judging the engine state by detecting the engine speed as mentioned above, the rotational angular speed of a ring gear or a plate mounted on the crankshaft is detected. Such a method is effective in a comparatively low engine speed area. In a high engine speed area, however, variations due to the pitch fabrication error of the ring gear or the plate are significantly presented between the cylinders. The effect of the pitch error thus makes it inconveniently impossible to judge the combustion state of the internal combustion engine accurately.
For overcoming the above-mentioned inconvenience, the present applicant has proposed in Japanese Patent Application Publication No. JP-A-9-72241 a means for detecting a value corresponding to the pitch error during normal combustion to correct the engine speed signal. Specifically, the proposed means calculates a combustion state parameter from a timing signal associated with the crankshaft rotation by a predetermined angle, and the timing signal is corrected from the variations of the combustion state parameter for normal combustion. In this method, a reference cylinder is determined, the amount of correction of the timing signal for a cylinder group including the reference cylinder and a cylinder opposed thereto is reduced in the case where the combustion state parameter for normal combustion of the particular cylinder group is not less than a predetermined value, and the amount of timing signal correction is increased otherwise. The timing signal thus is corrected according to the correction amount thus determined, and the combustion state parameter is calculated using the corrected timing signal.
The conventional technique proposed as above, in which the timing signal is corrected according to the variations of the combustion state parameter for normal combustion, can detect the combustion state of the internal combustion engine without being affected by the pitch fabrication error of the ring gear or the plate even in high engine speed area. Nevertheless, the response for calculation of the correction amount and and the stability of the correction amount calculated have yet to be improved.
The prevent invention has been developed for obviating the above-mentioned problem, and the object thereof is to provide a combustion state detection system for an internal combustion engine, in which the combustion state can be accurately detected in all engine operating areas (especially, in high engine speed area) where a positive torque is generated, and especially in which the response and stability are secured in the calculation of the correction amount used for correcting the timing signal detected, while at the same time detecting a misfire positively.